Device for converting a rotational movement into an axial movement

ABSTRACT

A device for converting a rotary motion into an axial motion has a threaded spindle ( 1 ), a nut concentrically surrounding the threaded spindle with a clearance and a plurality of axially parallel rollers ( 2 ) guided in a cage ( 6 ) and arranged in the clearance, said rollers ( 2 ) have a circumferential profile by which they mesh with the external thread of the threaded spindle ( 1 ) and with the corresponding internal thread of the nut. Each of these rollers ( 2 ) is axially displaceable within the cage ( 6 ) by the dimension of the thread pitch during a rotation of the nut relative to the threaded spindle ( 1 ), while at the end of such a rotation, each roller ( 2 ) is re-displaceable within an axial groove ( 7 ) of the nut into the starting position by a cam ( 8, 12 ) arranged in the vicinity of each end face of the cage ( 6 ). According to the invention, the nut is a thin-walled sheet metal sleeve ( 3 ) made by non-chipping shaping. In this way, a device with a simpler structure and more economic to manufacture is obtained.

FIELD OF THE INVENTION

The invention concerns a device for converting a rotary motion into anaxial motion, which device has a threaded spindle, a nut concentricallysurrounding the threaded spindle with a clearance and a plurality ofaxially parallel rollers guided in a cage and arranged in the clearance,said rollers have a circumferential profile by which they mesh with theexternal thread of the threaded spindle and with the correspondinginternal thread of the nut, each of said rollers is axially displaceablewithin the cage by the dimension of the thread pitch during a rotationof the nut relative to the threaded spindle, while at the end of such arotation, each roller is re-displaceable within an axial groove of thenut into the starting position by a cam arranged in the vicinity of eachend face of the cage.

BACKGROUND OF THE INVENTION

Such roller screw drives for converting a rotational motion into atranslational motion are used mainly in cases in which, for operationalreasons, no high precision of pitch and position is required but rather,an economic solution with a high degree of efficiency and good bearingcapacity. Such a roller screw drive is known from DE-OS 21 50 739. Thisdrive comprises a solid nut body and two likewise solid annular cammembers which mesh by regions having annular cam surfaces with annularend recesses of a cage for the rollers. The manufacturing of this deviceis highly complicated so that the resulting construction is veryexpensive.

SUMMARY OF THE INVENTION

The object of the invention is to create a roller screw drive which hasa simpler structure and is more economic to manufacture.

The invention achieves this object by the fact that the nut is athin-walled sheet metal sleeve made by non-chipping shaping which ispressed into a bore of the housing which receives the device. Thispermits a considerable reduction of material so that the device also hasa lesser weight. Due to being pressed in, the thin-walled sheet metalsleeve receives its precision of shape and dimension.

The sheet metal sleeve can be drawn from a circular blank. During thedrawing process, the axial groove for the return displacement of therollers can be formed at the same time. The internal thread of the sheetmetal sleeve can be made by roller-burnishing.

It is, however, also possible to make the sheet metal sleeve by bendingout of a sheet metal strip on which an internal thread has previouslybeen made by rolling, and then welding the thus formed sleeve along theabutting edges. One of the cams for the return displacement of therollers can be formed on a flange of the sheet metal sleeve and afurther cam for the return displacement of the rollers can be configuredon a disc inserted into and fixed in the sheet metal sleeve. A discprofiled by non-chipping shaping is suitable for this purpose. Bybending over an adjacent rim of the sheet metal sleeve, the disc can beaxially fixed in the sheet metal sleeve. It is also possible to fix thedisc axially in the sheet metal sleeve by swaging the material of thedisc and/or the material of the sleeve.

The thread of the spindle and the groove profile of the rollers can alsobe made by roller-burnishing.

By the pressing-in of the device into the bore of the housing, therequired radial clearance and pre-tension of the roller screw drive isobtained. If necessary, a selective matching of rollers and spindles canbe carried out.

BRIEF DESCRIPTION OF THE DRAWINGS

An example of embodiment of the invention is represented in the drawingsand will be described more closely in the following. The figures show:

FIG. 1, a partial representation of a device of the invention pressedinto the bore of a housing, in an axial section;

FIG. 2, a partial perspective view of a sheet metal sleeve of the deviceof the invention with an inserted roller.

DETAILED DESCRIPTION OF THE DRAWINGS

A device of the invention for converting a rotary motion into an axialmotion comprises a threaded spindle 1 surrounded on its outer peripheralsurface by a plurality of rollers 2 spaced behind one another. Therollers 2 are arranged axially parallel to the threaded spindle 1 andcomprise a profile by which they mesh both with the external thread ofthe threaded spindle 1 and with the internal thread of a nut which isarranged concentric to the threaded spindle 1 and surrounds this with aclearance corresponding to the rollers 2.

According to the invention, this nut is configured as a sheet metalsleeve 3 made by non-chipping shaping. The internal thread of thissleeve 3 can be made by roller-burnishing. The sleeve 3 is pressed intoa bore 4 of a housing 5 which can be a component to be displaced in theaxial direction of the threaded spindle 1. This pressing-in gives thesheet metal sleeve 3 its precision of shape and dimension.

The rollers 2 which surround the threaded spindle 1 are guided withinthe sheet metal sleeve 3 in a cage 6. When the threaded spindle 1rotates, the rollers 2 execute a planetary motion about the threadedspindle 1 within the sheet metal sleeve 3 and move at the same time intheir recesses in the cage 6 in an axial direction in keeping with thepitch of the thread of the threaded spindle 1. After a complete rotationof the threaded spindle 1, each roller 2 has moved in axial direction bythe dimension of the thread pitch of the threaded spindle 1 and has tobe returned to its starting position. For this purpose, the sheet metalsleeve 3 comprises an axially parallel groove 7 into which the roller 2comes to be situated after the rotation. In this position, the roller 2no longer meshes with the threaded spindle 1 and is returned by a camfixed in the sheet metal sleeve 3 to its starting position to then cometo mesh anew with the threaded spindle 1 during the next rotationthereof.

Such a cam 8 is formed on a flange 9 of the sheet metal sleeve 3 in thevicinity of one end of the cage 6. A disc 10 is inserted into the sheetmetal sleeve 3 in the vicinity of the other end of the cage 6, and afterthe flange 11 provided in this region has been bent over, the disc 10 isfixed in the sheet metal sleeve 3. This disc 10 comprises the second cam12 of the device. Depending on the direction of rotation of the threadedspindle 1, either the first cam 8 or the second cam 12 acts on theroller 2 to return it into its starting position.

What is claimed is:
 1. A device for converting a rotary motion into anaxial motion, which device has a threaded spindle (1), a nutconcentrically surrounding the threaded spindle with a clearance and aplurality of axially parallel rollers (2) guided in a cage (6) andarranged in the clearance, said rollers (2) have a circumferentialprofile by which they mesh with the external thread of the threadedspindle (1) and with the corresponding internal thread of the nut, eachof said rollers (2) is axially displaceable within the cage (6) by thedimension of the thread pitch during a rotation of the nut relative tothe threaded spindle (1), while at the end of such a rotation, eachroller (2) is re-displaceable within an axial groove (7) of the nut intothe starting position by a cam (8, 12) arranged in the vicinity of eachend face of the cage (6) characterized in that the nut is a thin-walledsheet metal sleeve (3) which is made by non-chipping shaping and ispressed into a bore (4) of a housing (5) which receives the device.
 2. Adevice according to claim 1, characterized in that the sheet metalsleeve (3) is drawn from a circular blank, and the axial groove (7) forthe return displacement of the rollers (2) is simultaneously formedduring the drawing process.
 3. A device according to claim 1,characterized in that the internal thread of the sheet metal sleeve (3)is made by roller-burnishing.
 4. A device according to claim 1,characterized in that the sheet metal sleeve (3) is bent from a sheetmetal strip on which the internal thread is made by rolling, andabutting ends of the sheet metal strip thus obtained are weldedtogether.
 5. A device according to claim 1, characterized in that one ofthe cams (8, 12) for the return displacement of the rollers (2) isformed on a flange (9) of the sheet metal sleeve (3).
 6. A deviceaccording to claim 1, characterized in that one of the cams (8, 12) forthe return displacement of the rollers (2) is formed on a disc (10)which is inserted into and fixed in the sheet metal sleeve (3).
 7. Adevice according to claim 6, characterized in that the disc (10) isaxially fixed in the sheet metal sleeve (3) by bending over an adjacentflange (11) of the sheet metal sleeve (3).
 8. A device according toclaim 6, characterized in that the disc (10) is axially fixed in thesheet metal sleeve (3) by swaging the material of the disc (10) and/orthe material of the sheet metal sleeve (3).